(1) Field of the Invention
This invention relates to a light-emitting device for constituting a large-screen display device to be used for a stadium or the like.
(2) Description of the Prior Art
Referring to FIG. 1, there is shown an exploded perspective view of a display device according to the prior art, as for example disclosed in Japanese Patent Application Laid-Open (KOKAI) No. 64-995 (1989). In the figure, reference character 1a denotes a front panel which is coated with a fluorescent material so as to function as a display portion, reference character 1b denotes a box-like spacer to which the display portion 1a is attached as a cover face, and 1c denotes a back panel attached to the spacer 1b as a bottom face of the box and serving as a substrate on which various control electrodes are mounted. These members are combined together to constitute a vacuum vessel of a display tube. Line form cathodes 2 are provided on the substrate 1c, together with first control electrodes (scanning electrodes) 3 and second control electrode (data electrodes) 4. Wiring patterns 5 and 6 are provided for common interconnections of the two kinds of control electrodes 3 and 4 in a row direction and a column direction, respectively. A shielding electrode 7 is provided with apertures 8 corresponding to light-emitting portions. Numeral 9 denotes a fluorescent material, and 10 an exhaust portion. FIG. 2 illustrates the layout and wiring of the two kinds of control electrodes 3 and 4. Reference characters S1 to S4 denote lead portions of the scanning electrodes 3, which are interconnected in common in the row direction, and D1 to D4 denote lead portions of the data electrodes 4, which are interconnected in common in the column direction. FIG. 3 shows the timings of signals which are impressed on the control electrodes 3 and the data electrodes 4. FIG. 4 shows an arrangement of pixels P11 to P14 and the correspondence thereof with the electrodes, and FIG. 5 illustrates the potential of each electrode and the flow of electrons. Furthermore, FIG. 6 shows an example of a display having a multiplicity of arrayed light-emitting devices (two of them are shown), and FIG. 7 is a fragmentary sectional view of the light-emitting device.
The fundamental principle in operation of this type of display device is that thermions emitted from the cathode 2 are accelerated to collide against the anode, whereby the fluorescent material applied to the anode surface is excited to emit light. In FIG. 5, the behavior of the thermions emitted from the cathode 2 depends on the combination of the potentials at the first control electrode (scanning electrode) 3 and the second control electrode (data electrode) 4. That is, the thermions behave in the manner as described below (the description is made with reference to FIG. 5).
[1] When the scanning electrode 3, interconnected in the row direction, and the data electrode 4, interconnected in the column direction, are both positive in potential relative to the cathode 2:
The electrons emitted from the cathode 2 by the positive potential of the data electrode 4 are deflected by the potential of the scanning electrode 3 so as to pass through a predetermined aperture and reach the anode, thereby causing the fluorescent material 9 to emit light. PA1 The negative potential of the data electrode 4 closer to the cathode 2 renders the potential in the vicinity of the cathode 2 negative, whereby emission of thermions is restrained. Therefore, the fluorescent material 9 does not emit light. PA1 (a) When the scanning electrode 3 on the other side is positive, the thermions emitted from the cathode 2 are deflected by the potential of the scanning electrode 3 to the side of the other scanning electrode 3, so that the fluorescent material 9 does not emit light. PA1 (b) When the scanning electrode 3 on the other side is also negative, the potential in the vicinity of the cathode 2 becomes negative under the influence of the negative potential of the scanning electrodes 3 on both sides, because the data electrode 4 having the positive potential is small in area. Therefore, the emission of the thermions is restrained, and the fluorescent material 9 does not emit light. PA1 The potential in the vicinity of the cathode 4 becomes negative, so that the emission of thermions is restrained, and the fluorescent material 9 does not emit light.
[2] When the scanning electrode 3 is positive and the data electrode 4 is negative:
[3] When the scanning electrode 3 is negative and the data electrode 4 is positive, there are two situations:
[4] When both the scanning electrode 3 and the data electrode 4 are negative:
Taking into account the relationship between the interconnection shown in FIG. 2 and the array of pixels shown in FIG. 4, therefore, fluorescent light is emitted from the fluorescent materials 9 located at intersections of the row (scanning) electrodes and column (data) electrodes which are supplied with positive potentials. First, when a signal is impressed on the lead portion S1, the pixels P11 to P14 are selected for emitting light according to the potential of the lead portions D1 to D4 of the data electrodes. Next, with a signal applied to the lead portion S2, the pixels P21 to P24 are similarly selected for emitting light according to the potential at the data electrodes. Namely, as shown in FIG. 3, an arbitrary display can be obtained by applying a serial scanning signal to the scanning electrodes 3 and appropriate data signals to the data electrodes 4. FIG. 6 shows an example of a display in which a multiplicity of light-emitting devices A are arrayed. In order that the joint between two light-emitting devices A may be inconspicuous, a space T2 not less than two times the dead space (width: T1) at the periphery of each light-emitting device A should be present between pixels in the device A. FIG. 7 shows a fragmentary sectional view of the light-emitting device A. A front panel 1a is coated with a fluorescent material 9 by screen printing. Practically, an aluminum film is vapor-deposited on the surface of the fluorescent material 9, though not shown in the figure. Further, a spacer 1b and a back panel 1c are sealed with frit glass 50. Control electrodes 20 for letting signals out of the light-emitting device A are led out through the seal portion between the spacer 1b and the back panel 1c, as shown in FIG. 1, but the electrodes 20 may be led out directly from the back panel 1c. The joining of the front panel 1a and the spacer 1b is, as shown in FIG. 8, carried out by moving a dispenser 31 once along the entire length of the joint surface of the spacer 1b while ejecting the frit glass 50 from a nozzle 32 of the dispenser 31, and pressing the frit glass 50 supplied on the spacer 1b against the front panel 1a. The joining of the back panel 1c and the spacer 1b is performed in a similar manner.
The light-emitting devices according to the prior art have the construction as above. Therefore, in order to achieve a close arrangement of the light-emitting devices A and thereby obtain normal images, uniformity of the pixel arrangement in a display should be maintained with high accuracy as shown in FIG. 6. According to the prior art, however, the frit glass 50 at the seal portion between the front panel 1a and the spacer 1b would flow onto the fluorescent material 9 of the display portion 1a, as shown in FIG. 8, thereby damaging the uniformity of the pixel arrangement. There has also been the problem that the frit glass 50 would flow out to the outer side of the spacer 1b, thereby hindering close arrangement of the light-emitting devices A. The flowing-out of the frit glass 50 arises from the uneven coating amount of the frit glass 50 due to the use of the dispenser 31, as shown in FIG. 8, for application of the frit glass 50. For example, the dispenser 31 is moved once along the joint portion (the portion to be coated with the frit glass) of the spacer 1b while ejecting the frit glass 50 through the nozzle 32. In carrying out this operation, it is difficult to make constant both the quantity of the frit glass 50 ejected from the nozzle 32 and the moving speed of the dispenser, especially at corner portions of the spacer 1b. Consequently, the coating amount of the frit glass 50 varies from place to place, making it necessary, after the sealing step, to grind off the frit glass 50 protruding from the joint portions between the spacer 1b and the front and back panels 1a, 1c. Such a grinding step leaves minute flaws on the ground portions, thereby lowering the strength of the glass vessel, resulting in that the light-emitting device obtained cannot be guaranteed for long-term reliability.